1. Field of the Invention
The present invention relates to computers and display devices. In particular, the present invention relates to a method for producing a graphical mouse cursor on a display device while operating in text mode.
2. Description of Related Art
Conventional computer systems commonly use a display adapter and a display device to present information to the user. The display adapter and display device are coupled to a processing unit to produce the images on the display device. The processing unit is also coupled to an input device such as a keyboard or mouse-type controller to receive data from the user. The processing unit modifies the information shown on the display device in response to user manipulation of the input device.
One method used extensively in the art for producing images on a display device is referred to as text mode operation or a text user interface. FIG. 2 illustrates a screen display of a text user interface. The computer displays information using letters, numbers, and punctuation. The standard IBM set of characters and symbols is illustrated in FIG. 4. The text user interface can use special symbols (e.g. a happy face and lines) to create graphical images to a limited degree. However, because the character set is limited, typically to 256 characters, the capability for producing graphical images is severely restricted.
In text mode operation, the screen is divided into a fixed grid, usually 80 columns by 25 lines. Each position in the grid provides an area for the display of a character or symbol. The display adapter controls the video screen, and in "text mode" is also responsible for converting characters into the actual dots that appear on the screen. For example, the processing unit of the computer provides a signal representing the character to be produced on the display at a given row and column, and the display adapter generates the appropriate pattern of dots on the video screen for the signal from the processing unit. Because only a relatively small amount of information must be processed (only 2000 characters per screen at 80 by 25), text user interfaces are very fast and memory efficient.
Another method used to produce images on a display device is the graphics mode or a Graphical User Interface (GUI). An example of a screen displaying a graphical user interface is shown in FIG. 3. A GUI is produced by controlling each individual screen dot, thereby allowing any type of character or graphic image to be displayed. In graphics mode, the processing unit of the computer system is responsible for managing all of the individual dots. The display adapter provides no assistance in forming characters when in graphics mode. Since GUIs force the processing unit to handle a large volume of data (over 300,000 dots on the average PC screen), they are slower and require more memory than text user interfaces. The memory and processing overhead prevents most older computers from using a GUI, and even on newer computers many users prefer the higher speed and memory efficiency of a text interface.
Another difference between a text user interface and a GUI is the display and movement of the cursor. On a GUI, the cursor usually looks like an arrow, and it moves smoothly across the screen as the user moves the mouse. On a text system, the cursor is a rectangular block displayed in a different color than the rest of the data. Because text systems have a fixed display grid (80 by 25), the movement of the cursor appears "choppy"60 and doesn't always reflect the actual motion of the mouse. This lack of precision detracts for the usefulness of the mouse.
Therefore, there is a need for a method for producing a mouse-type cursor that has smooth movement and improved precision without significantly reducing processing speed and requiring large amounts of memory.